1. Field of the Invention
The present invention relates to a system and method for inspecting articles such as wafers, reticles and the like.
2. Description of the Related Art
The inspection of semiconductor wafers is typically performed by scanning a laser beam across a wafer's surface and collecting light scattered therefrom. The scanning operation is conducted by scanning the laser beam across the wafer surface in a first direction using one of a variety of known deflectors, such as acousto-optic deflectors or electromechanical deflectors, while moving a stage that supports the wafer thereon in a second direction that is typically orthogonal to the first direction.
Another type of inspection includes illuminating an area and acquiring an image. U.S. Pat. No. 5,699,477 of Alumot el al provides an example of such inspection systems.
There are various devices and methods for scanning a laser beam, such as acousto-optic devices, electromechanical deflectors, and the like. There is a greater emphasis on the throughput of inspection device and accordingly on the throughput of scanners, as the design rules for semiconductors rapidly shrink without a corresponding decrease of the inspection sequence time period or the overall size of semiconductor dies or wafers.
High throughput inspection systems utilize optical beam arrays as well as electron beam arrays for increasing throughput. Hybrid systems that include electron beam illumination, electro-optical conversion and light beam detection are also known. Electron beams also provide higher resolution. U.S. Pat. No. 6,671,042 of Almogy, U.S. Pat. No. 6,639,201 of Almogy et al., U.S. Pat. Nos. 6,578,961 and 6,208,411 of Vaez-Iravani and U.S. Pat. No. 6,248,988 of Krantz, which are incorporated herein by reference, describe state of the art inspection systems.
Some prior art inspection systems utilize relatively large objective lenses and additional optical components in order to capture a large field of view (FOV). The complexity and cost of lenses as well as their development period increases in a non-linear manner as their respective size grows.
Various image processing methods are known in the art. They include die-to-die comparison, cell-to-cell comparison and die to database comparison.
There is a need to provide an efficient system and method for high throughput inspection.